Of the three main fossil fuels – coal, petroleum and natural gas – it could be argued that petroleum is the most versatile.
Coal is a powerful source of heat, well suited to heating buildings and providing power for industrial processes. But it leaves residue, and transporting coal can be a dirty and cumbersome process due to its bulk and weight. For these same logistical reasons, its uses are limited; coal could not, for instance, be used to fuel small vehicles. Natural gas burns cleanly and efficiently and weighs practically nothing, but it requires specialist handling. Petroleum, or crude oil, is neither as cumbersome as coal nor as volatile as natural gas. It can be used to heat buildings, power internal combustion engines, and produce electricity, and it also has numerous non-fuel applications.
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How Crude Oil Is Formed
Crude oil is the fossilised remains of small marine creatures that died many millions of years ago, accumulated at the bottom of the ocean, were covered by sand, mud and silt, and became buried beneath the sea bed. As more and more silt was deposited above them, the layers of organic material were compressed into liquid hydrocarbons, or crude oil. Due to continental drift, oilfields are now found below ground in areas that are no longer covered by the sea.
The crude oil in an oil field is a mixture of many different hydrocarbons. Each has different characteristics; some crude oils are pale in colour and of a similar viscosity to water, and some have a very thick consistency and a dark colour. According to its composition, each of the different hydrocarbons, called ‘fractions’, will be suited to a particular kind of application.
Natural gas often occurs alongside crude oil, and the gas must be separated from the oil before the refining process can begin. Some hydrocarbons, such as methane and butane, are common to both gas and oil.
What Happens at Oil Refineries?
The first step is to separate the oil into its hydrocarbon fractions. This is done by fractional distillation. Each different fraction has a different boiling point. Therefore the crude oil is heated, and when the boiling point of one particular fraction is reached, this will vaporise. Once this vapour has been condensed and collected, the remaining oil can be heated again until the next boiling point is reached, and the process can be repeated.
Having being separated out, each hydrocarbon fraction undergoes chemical processing, initially to remove impurities. Further chemical processing can then be carried out. Some fractions will be blended to create specific consumer products, such as the different grades of petrol and diesel that are sold at garages, and in some cases additives will be included to add value to the product.
Chemical processing can also alter the structure to convert one hydrocarbon fraction into a different type, since fractional distillation of the crude oil tends not to yield up the largest quantities of the oils for which demand is highest. Some diesel, for instance, is likely to be converted into petrol, since out of all the derivatives of crude oil, petrol is in greatest demand.
The Many Different Uses of Crude Oil
By far the largest proportion of the energy we obtain from crude oil is destined for use as automotive fuel. There is a vast market for not only petrol but also diesel, for commercial vehicles and for public and personal transport. Kerosene is the basis of the aviation fuel used in jet aircraft.
Oil is used extensively for domestic and industrial heating, and also in power stations to generate electricity.
Petroleum gases such as butane and methane occupy a niche market in that they can be supplied as bottled gases for cooking and heating where there is no natural gas supply. Liquified Petroleum Gas (LPG), a mixture of butane and methane, is distributed at petrol stations for automotive use and can be supplied in bulk for heating applications. LPG provides an environmentally-friendly fuelling option because it has low emissions.
However, by no means all oil-based products are used as fuels. Petroleum also provides us with lubricants and the raw materials from which plastics and other polymers are manufactured.
The Future of Petroleum as an Energy Source
Our continuing heavy dependence on petroleum, despite rapidly escalating prices in recent years, gives rise to certain concerns. One is that, of all the fossil fuels, crude oil may run out first; some studies claim that oil reserves could reach a critical level within a generation, though others disagree. Another concern is the level of environmental pollution created by burning petroleum-based fuels, and its contribution to climate change. However, a lot of work has been done by car manufacturers and others to develop low-emission engines, and by oil refineries to remove impurities and pollutants from the oil.
